1. Field of the Invention
The present invention deals with a lighting unit designed for functional similarity to an incadescent light source, and more particularly with a lighting unit in which the principal source of light is an arc lamp supplemented by a standby filamentary light source, and which includes a compact "high frequency" power supply unit for supplying the needed energization from a conventional 120 volt 60 hertz source.
2. Description of the Prior Art
The present invention is an outgrowth of earlier efforts to produce an energy efficient and comparatively low cost replacement unit for the incandescent lamp. The incandescent lamp converts most of the electrical energy supplied into heat, a small percentage always less than 10% being converted into visible light. With the cost of energy rising, a need has arisen for a lighting unit whose conversion of electrical energy into light was substantially higher. Known lighting units such as fluorescent units have had double to quadruple the lighting efficiency of an incandescent light. A property of such devices, which has limited their more general application, has been the high initial cost of the ballast for powering such devices and their elongated configuration. Another possible alternative has been the high pressure discharge lamp having up to six times the efficiency of an incandescent lamp. High pressure metal vapor lamps have been available in high power units requiring costly power supplies, restricting their use to street lighting and commercial as opposed to home lighting. Recently, as disclosed in U.S. Pat. No. 4,161,672, smaller low wattage, metal halide lamps having efficiencies approaching those of the larger size have been invented. Such lamps are a potential energy efficient replacement for the incandescent lamp provided that convenient low cost provisions can be made for standby illumination and for supplying the diverse electrical requirements for the two light sources.
A prior solution to the problem of a replacement unit for an incandescent lamp is contained in the U.S. Pat. No. 4,232,252.
Another solution to the problem of a replacement unit for an incandescent lamp is contained in the cited application Ser. No. 47,972 filed June 13, 1979. The efficiency of the present arrangement is somewhat higher than that disclosed in the referenced Peil and McFadyen application.
The power supply of the present lighting unit represents an outgrowth of earlier high frequency power supplies in which a ferrite transformer, normally controlled for non-saturated operation, and a switching transistor are significant elements. Such power supplies have been termed static inverters in deference to the fact the "dc" quantities are converted to ac through static or non-moving parts. Patents dealing with inverters of this class and ferrite transformers having the saturation avoidance feature include the U.S. Pat. Nos. 3,914,680, 4,002,999, 4,062,390 and 4,004,251. U.S. Pat. No. 4,202,231 deals with a static inverter employing a single switching transistor in a blocking oscillator configuration and other related configurations.
The U.S. application Ser. No. 139,946 deals with a ferrite transformer having a saturation avoidance function of the type herein employed.